THIS INVENTION relates to a filtration system and a filter unit suitable for microfiltration, ultrafiltration or reverse osmosis.
According to the invention there is provided a filtration system which comprises a filter unit having a hollow housing which encloses at least one filter element, the filter unit having a feed fluid inlet opening into the interior of the housing and communicating with an upstream side of each filter element, a retentate outlet leading from said interior of the housing and communicating with said upstream side of each filter element, and a permeate outlet leading from the interior of the housing and communicating with a downstream side of each filter element, said permeate outlet being isolated from the retentate outlet and from the inlet by the filter element or elements, and the retentate outlet being spaced from the inlet and in communication therewith, and the system including at least one bundle made up of a plurality of releasably interconnected modular members, which bundle forms a flow control unit for controlling fluid flow through the filter unit from its feed fluid inlet to its permeate outlet.
In the various embodiments of the invention described hereunder, various combinations of features are described or defined as simultaneously forming part of the invention. It is explicitly noted, however, that it is not essential that the features of these combinations be used simultaneously, and the invention contemplates that any one or more of such features can be omitted or altered, while one or more of the remainder are retained. In particular, any feature may be omitted, without enlarging the invention of extending its scope, provided that the features defined hereinabove are present.
The system can thus be regarded as including one or more bundles, at least one of which is made up of a plurality of interchangeable modules in the form of modular members constructed and arranged to form a flow control unit for controlling fluid flow through the filter unit from its feed fluid inlet to its permeate outlet. At least some of said modular members will respectively be of different functions and constructions from the remainder of said modular members; and the flow control unit will be arranged to control flow through at least one of said inlet and outlets of the housing. By xe2x80x98modularxe2x80x99 is meant that the modular members or modules are capable of being interchangeably nested or stacked, face-to-face if they are flattened in shape, or end-to-end if they are elongate in shape, to form a bundle or stack, each member being of the same outline, when viewed in end elevation, so that the stack or bundle has a substantially constant cross-sectional outline along its length.
The flow control unit may be associated with the feed fluid inlet to the housing interior and with the retentate outlet from said interior, so that it controls the rate of fluid flow from the feed fluid inlet to the retentate outlet. Instead, the flow control unit may be associated with the permeate outlet from the interior of the housing, so that it control the rate of fluid flow out of the retentate outlet. In a particular construction the filtration system may have two flow control units, one associated with the feed fluid inlet to the housing interior and with the retentate outlet of the housing interior, on the one hand, and the other associated with the permeate outlet from the housing interior, on the other hand, so that there is control of the rate of fluid flow both from the rear fluid inlet to the retentate outlet, and fluid flow out of the retentate outlet. In other words, the system may include two bundles of modular members, which bundles respectively form two flow control units, one for controlling fluid flow from the feed fluid inlet to the retentate outlet, and another for controlling fluid flow through the permeate outlet.
Each flow control unit may be separate from the filter unit, being connected thereto by a fluid flow line, such as a pipeline, in which case each flow control unit may be physically remote from the filter unit. Preferably, however, at least one, and conveniently each, flow control unit is mounted on the housing or forms part of the housing. Thus, each bundle of modular members may be mounted on the housing.
The housing may be elongated, being open at at least one end thereof, each open end of the housing being provided with an end closure, and at least one said end closure may be in the form of a said flow control unit as described above, so that each interchangeable modular member can be regarded as a closure member forming part of a said end closure.
The housing may be in the form of a cylindrical hollow tube of circular or other suitable cross-section, eg of stainless steel, open at both ends, so that the filter unit has a said end closure at each end thereof, the end closures being respectively bolted to flanges provided therefor, at opposite ends of the tube, by a plurality of bolts, circumferentially spaced about the housing and holding the end closures up against opposite ends of the housing, to close the housing. In another embodiment, wherein the filter unit is of relatively short length, bolts extending from one end closure to the other may be used to hold the end closures up against the respective ends of the housing, to close the housing. In each case, however, the bolts conveniently act to hold the modular members of each bundle together to form a flow control unit which acts as a said end closure for the tube.
In each case, in general, the housing may be tubular, having at least one open end closed by an end closure in the form of a said bundle of modular members forming a flow control unit; and the housing may have two open ends, each closed by an end closure, at least one of the end closures being in the form of a said bundle of modular members forming a flow control unit.
More particularly, said flanges and end closures may be of square (or other suitable) outline, having bolt holes at the corners thereof, there being four bolts passing through said bolt holes and bolting the end closures to the flanges. The fluid inlet and the outlets preferably each pass through a said modular member; and the modular members will have the same outline as the end closures, being interchangeably stackable against one another in series, face-to-face. Thus, each modular member may be in the form of a square plate, of lesser or greater thickness as required for its function and construction, and having bolt holes at its corners. The filter unit will thus have, in this case, an end closure at each end of the housing, at least one said end closure being of composite construction and being made up of a plurality of said modular members, stacked face-to-face, sandwich fashion.
The end closures may each be provided with at least one sealed coupling passage to enable a plurality of filter units to be coupled together via the sealed coupling passage. Such plurality of filter units may be coupled together into any desired configuration, thereby to provide for series flow or for parallel flow or for a combination thereof, ie series/parallel flow or cascade-type flow.
Typically, there may be a single filter element of porous sintered ceramic material, the filter element having a plurality of passages in its interior, the passages extending alongside one another and being transversely spaced from one another, at least one of the passages being a filtration passage in communication with the feed fluid inlet and with the retentate outlet and at least one of the passages being a drainage passage, and each drainage passage being in communication with the permeate outlet and being isolated from each filtration passage. Instead, however, there may be a plurality of the filtration passages, the filter material acting as a filter membrane support and each filtration passage being lined with a filter membrane, there being a plurality of the drainage passages and the filter element having an outer surface the major part of which faces into a space between the filter element and the housing. When a said bundle of modular elements is mounted on the housing, the bundle may include a modular member in the form of a flow deflector member, the filter element having a plurality of filtration passages and the deflector member defining at least one fluid flow path for deflecting fluid flowing along a filtration passage in the filter element into another filtration passage in the filter element. In particular, the filter element may be elongate, the housing being elongate and the filter element extending along the interior of the housing, the filter element having a cross-sectional area equivalent to the area of a circle having a diameter of 40-200 mm, and the filter element having a length of 1.5-6 m.
In a particular embodiment of the invention there is thus a single filter element in the form of an elongated membrane support comprising a straight sintered ceramic extrusion, eg a circular-cylindrical sintered xcex1-alumina extrusion, the filter element having a plurality of transversely spaced passages extending along its length, conveniently straight and parallel to one another. At least one, and, as indicated above, usually a plurality, of these passages will each be a filtration passage, optionally being lined with a filter membrane which may be sintered to the inner surface of the passage, each filtration passage being on the upstream side of the filter element and in communication with the fluid inlet and with the retentate outlet. Optionally, one or more of the passages may be a drainage passage, each drainage passage being isolated from the filtration passage and being on the downstream side of the filter element, in communication with the permeate outlet, the outer surface of the filter element facing into a space between the filter element and the housing which is also in communication with the permeate outlet. Instead, if desired, each filter element or membrane support may be of another material, such as fabric, paper, a plastics material, porous stainless steel or other metal which may be sintered, another sintered ceramic, or the like.
As indicated above thexe2x80x94alumina support typically has a diameter of  greater than 40 mm, usually 40-200 mm, eg about 100 mm, and a length of 1.5-6 m, usually 1.5-2.5 m, eg 2 m. The filtration passages may all be of the same diameter and may be of the same size or smaller than the drain passage or passages, all the drain passages, if there are several, being of the same diameter. The diameters of the filtration passages and drain passages may be in the range 2-20 mm, usually 4-14 mm, eg about 10 mm. The filtration passages may be arranged so that, viewed in end elevation, there are concentric circular rows of filtration passages, the filtration passages of each row being circumferentially spaced in series from one another and the rows being radially spaced from one another, each row being concentric with the axis of the support. The outermost row may have the most said filtration passages therein, the next row radially inwardly therefrom having fewer said passages, and the number of passages in the rows decreasing progressively radially inwardly from row to row, so that the innermost row has the fewest passages. The filtration passages may be more or less equally spaced from one another and the rows may be more or less equally spaced form one another by the same spacing as that between the passages, and the spacings between the rows, between the innermost row and the drain passage and between the outermost row and the support outer surface, may be more or less the same or equal. In the case of a circular-cylindrical ceramic filter element, the filter element may be concentrically mounted in the housing tube with an annular space therebetween, each end of the tube being held by a plurality of circumferentially spaced spacers, which may be elastomeric, and which project radially inwardly from the housing to engage curved outer surface of the support to hold it concentrically in the housing tube. The housing may be made of two portions, eg the housing tube and a collar at one end of the tube, one of said portions, eg the collar, being receivable spigot/socket fashion in the other so that it is telescopically slidable therein, the radial space between the housing portions being sealed by a peripheral seal which permits the one portion to slide telescopically and sealingly within the other, to alter the length of the housing to cater for unequal changes in length of the housing and in the length of the support, arising from unequal thermal expansion thereof. In other words, the housing may be made up of two portions, one of which is received spigot-socket fashion in the other, being telescopically slidable therein and sealed thereto, to permit unequal thermal expansion of the housing and each filter element enclosed therein.
A seal such as a disc-like elastomeric sealing pad may be provided at each end of the ceramic element, sandwiched between said end and the adjacent end closure and, if there is a bundle or stack of modular members forming a composite end closure at one or each end of the ceramic element, there may be a similar elastomeric pad between each adjacent pair of modular members. Each said pad will have flow apertures therethrough, registering with the ends of the passages in the filter element, and/or registering with flow passages through the modular member or members in contact therewith, as the case may be. Suitably located springs, such as disc springs, may be provided to keep the pads under compression in the axial direction of the filter element, to promote good sealing by said pads and to cater for said unequal thermal expansion between the filter element and the housing tube. Instead, or in addition, the filter element or support may be sealed to the housing, at the end of the support remote from the permeate outlet, by an O-ring seal or a diaphragm-shaped peripheral elastomeric seal under compression between the support and the housing, so that the seal is deformed and seals effectively, whether or not there is a pressure drop in either direction across it.
At each end of the filter element there may be at least one modular member in the form of a flow deflector plate for deflecting fluid flow issuing from a plurality of filtration passages at that end of the filter element into a plurality of other filtration passages so that there is flow reversal, i.e. so that the fluid flows along said other passages in the opposite direction along the filter element. Each deflector plate may thus have a plurality of grooves or elongated depressions or cavities on its axially inwardly facing surface for this purpose, each groove being arranged on said surface so that it receives said fluid issuing from at least one of said plurality of passages, and channels it into a said other passage. Instead, each deflector plate may be provided with a plurality of passages for this purpose, registering with said filtration passages.
It will be appreciated that the grooves can be arranged to provide for flow along all the passages in series with one another, or to provide for series/parallel flow whereby a plurality of groups of passages are provided, flow along the groups being in parallel and flow along the passages of each group being in series. Furthermore, the grooves can be arranged for cascade flow, whereby fluid issuing from said plurality of passages is deflected into a plurality of other passages, the number of other passages into which the fluid is deflected being fewer than the number of passages from which it issues. One or more cascades can be provided in this fashion, eg a plurality of cascades in parallel with one another. Naturally, if deflector plates are omitted entirely, the filter element can provide for parallel once-through flow of fluids. The filtration passage or passages at the upstream end of each series or cascade will be in communication with the filter unit feed fluid inlet, and the filtration passage or passages at the downstream end of each series or cascade will be in communication with the retentate outlet.
In filter units of the type in question provision is often made for one or more of back-pulsing with optional intensification thereof, backwashing, steam sterilization, sponge-ball cleaning of debris from the filtration passages, throttling of the retentate outlet to pressurize the fluid on the upstream side of the filter element, and the like, such provision requiring the provision of various flow control valves. Accordingly, the system of the present invention may provide for one or more of these features, one or more of the modular members containing the flow lines and the valves required therefor, these modular members being sandwiched face-to-face and forming part of one or the other end closure for the housing tube. Preferably, the flow lines are defined by cavities and/or passages within the modular members and the valves are located within such cavities or passages. Furthermore, the system may include a modular member provided with catch pots which contain sponge-balls, together with a modular member containing a valve bridge for reversal of the direction of flow through the filtration passages when they are arranged in series, for fluid flowing from the feed inlet via the catch pots and filter element to the retentate outlet; it may include a modular member provided with a steam inlet line; it may include a modular member comprising a programmable electronic controller or microprocessor for valve operation; it may include a modular member provided with a back-pulse intensifier; it may include a modular member provided with a back-pulse accumulator; it may include an intensifier modular member provided with a pressure intensifier or fluid capacitor defining a fluid reservoir; it may include a flow reversal modular member provided with a flow reversal valve for reversal of the direction of fluid flow through the filter element; it may include a modular member containing a back-pulse flow line for connection to an internal or external back-pulse accumulator unit; and one or more modular members may be provided with one or more valves for connecting the downstream side of the filter unit with the steam inlet line, with the back-pulse flow line, with the back-pulse intensifier, and/or with the permeate outlet, as the case may be.
The throttling valve for the retentate outlet may be of any suitable construction and may be operated by an electric motor via a suitable drive. The remaining valves are preferably of the elastomeric tubular sleeve type, co-operating with an internally mounted caged torpedo, operable by external fluid pressure on the sleeve to pinch it on to the torpedo to close the valve, said fluid pressure optionally being supplied by the fluid feed via a solenoid valve. The throttling and other valves may be controlled by said electronic controller or microprocessor, which may have inputs with regard to fluid temperature, with regard to fluid pressure and with regard to fluid flow rate, derived from sensors therefor mounted in one or more of the modular members.
In one particular embodiment of the filter unit, the filter unit may be provided with a flow reversal modular member forming part of each end closure, with the flow apertures in the flow reversal modular members registering with the ends of the passages in the filter element.
As mentioned above, the modular members may be of modular configuration and can be sealingly coupled together in series, with the aid of sealing pads, at each end of the filter unit, to make up the respective end closures there.
In another particular embodiment, the filter unit may be provided with a flow reversal modular member having passages provided therein arranged to permit control of flow reversal by means of opening or closing a plurality of, eg four, valves located in said passages. The valves may be of the type actuated by fluid pressure to permit rapid opening or closing thereof, such as valves having a flexible sleeve as described above, eg torpedo type valves. The filter unit is also in this case preferably provided with at least one modular member having catch pots and sponge balls.
According to a further embodiment of the filter unit, the filter unit may include an intensifier modular member or fluid capacitor modular member forming part of one of the end closures, with the intensifier modular member defining a fluid reservoir for containing pressurized fluid and being in fluid communication with the filtration system and having a fluid outlet connected by means of passages and valves provided in said intensifier modular member and/or in one or more additional modular members, to provide high-pressure back-pulsing of fluid through the modular members on the downstream side of the filter element. The intensifier modular member may be provided with a piston defining a wall of the fluid reservoir which is displaceable to permit transfer of pressure from the fluid in the filter system to the fluid in the reservoir. Preferably, the diameters of the portion of the piston and sleeve on the fluid reservoir side are smaller than those of the portion of the piston and the sleeve in fluid communication with the filtration system. Preferably, the valves in this embodiment are actuated electronically in response to programmed instructions or in response to automatic sensing of measured signals such as fluid pressure and/or fluid flow rate in the filtration system, to control back-pulsing.
According to a further embodiment, the filter unit is provided with a sterilization modular member provided with a steam inlet line, this modular member being located on the downstream side of the filter element and steam flow into the filter element being controlled by means of valves provided in said modular member.
In another preferred embodiment, the filter unit is provided with an integrated electronic control system or electronic controller which is electronically- or fluid-actuated. The electronic control systems may detect or measure fluid- or filter unit variables, such as at least one of pressure, volume and temperature, to thereby actuate, in the correct or desired sequence, various modular members and valves to control the operation of the filter unit, eg for sterilization, back-pulsing, etc., or to control the operating pressure of the filter unit. Preferably, the control system is programmed by means of suitable algorithms to enable the control system to decipher or respond to input signals or measurements, thereby to determine the desired response and to control the filtration.
The invention also extends to a filter unit which comprises a preferably elongated hollow housing which is provided at opposite ends thereof with respective end closures, the housing enclosing at least one filter element comprising sintered ceramic material, the unit having a feed fluid inlet opening into the interior of the housing and communicating with an upstream side of the or each filter element, a retentate outlet leading from the interior of the housing and communicating with said upstream side of the or each filter element, and a permeate outlet leading from the interior of the housing and communicating with a downstream side of the or each filter element, said permeate outlet being isolated from the retentate outlet and from the inlet by the filter element or elements and the retentate outlet being spaced from the inlet and in communication therewith, the housing comprising two portions telescopically slidable relative to each other and sealed together by a peripherally extending seal therebetween which permits one said portion to slide longitudinally within the other.
While the construction of the filter unit, and the various features which it may have, may generally be as described above for the system of the present invention, in a particular embodiment of the filter unit there is a single filter element or support which has a diameter of  greater than 40 mm, eg up to 100 mm or more and a length of  greater than 1500 mm, eg 2-6 m, having a plurality of filter passages extending along its length. The support, in a particular embodiment which is described in detail as an example to illustrate the invention, may have one or more drainage passages extending along its length. In particular, the support may have 20 or more filtration passages, eg about 40, arranged in radially spaced concentric circles of circumferentially spaced passages about the axis of the support, which is conveniently circular in cross-section, when viewed in end elevation, the outermost ring having the most passages and the number of passages in each circle decreasing progressively from circle to circle in the radially inward direction of the support, so that the innermost ring has the fewest passages. The passages may be more or less equally spaced from one another and from the outer surface of the support. Conveniently there is a single central drainage passage, of the same diameter or larger than the filtration passages, which are preferably all of the same diameter. At least one of the end closures may be in the form of a bundle made up of a plurality of releasably interconnected modular members, the bundle optionally forming a flow control unit for controlling fluid flow through the filter unit from its feed flow inlet to its permeate outlet. The other end closure may be a simple wall, or it may be another bundle made up of a plurality of releasably interconnected modular members.
It will be appreciated that, although separate modular members have been described above with separate functions, several functions may be contained in a single modular member.
The invention also provides a novel flow control unit comprising a bundle of modular members as described above, for connection to hollow housing of a filter unit, either via a flow line or mounted on the housing to form part of the filter unit.
The filtration system of the present invention is expected usually to be controlled so as to meet a certain range of recovery ratios with a given system input. In this regard a recovery ratio is defined as the ratio of a quantity of feed which is filtered out by a filter, ie the filtrate, to the total feed to the filter. The quantity of feed which is not filtered out by the filter is the retentate. The recovery ratio is usually expressed as a percentage, eg 80% recovery means that there is 80% filtrate and 20% retentate after filtration. Thus an 80% recovery ratio will take place when the retentate flow rate is 20%, and the filtrate flow rate is 80%, of the feed rate into the system. During use, filters of the type in question often become clogged, and it then becomes necessary to control the recovery ratio by controlling the exit rate at which the retentate issues from the filter.
The filtration system of the present invention may conveniently be controlled by the control method and controller of the Applicant""s co-pending application Ser. No. 09/722,161.